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Abstract:

The present disclosure relates to an electrical heating device for motor
vehicles, in particular with electrical propulsion. The heating device
uses a PWM based control concept which can be used for heating elements
with any non-linear characteristics. In this respect, activation times in
a cycle frame are assigned to power stages to be controlled and are
stored in a table in a non-volatile memory.

Claims:

1. An electrical heating device for heating fluids for motor vehicles,
wherein the heating device comprises: an electrical heating stage with at
least one heating element; a control device for adjusting a heating power
in fine steps by modulating he current flowing through the heating stage;
and a non-volatile memory for storing an assignment table which assigns a
time period for the activation of the electrical heating stage to each
power stage in a plurality of specified power stages; wherein the control
device activates the current flowing through the electrical heating stage
for the time period assigned to a power stage in the assignment table
within a specified cycle frame in order to adjust the heating power of
the electrical heating stage.

2. The electrical heating device according to claim 1, wherein the
relationship between the time periods stored in the assignment table and
the power values of the assigned power stages of the first electrical
heating stage is non-linear.

3. The electrical heating device according to claim 1, wherein the time
period is specified as a mark-space ratio in a percentage of the duration
of the specified cycle frame in the assignment table.

4. The electrical heating device according to claim 1, further
comprising: at least one further electrical heating stage with at least
one heating element; wherein the heating power of the further electrical
heating stage can be switched only between zero and a maximum power, and
the heating power can be separately adjusted by the control device for
the electrical heating stages by adjusting the current flowing through
each of the electrical heating stages.

5. The electrical heating device according to claim 1, wherein the
non-volatile memory is a programmable read only memory.

6. The electrical heating device according to claim 1, further
comprising: a device for the measurement of the total heating current
flowing through the heating device; and a calculation device for
calculating a momentary heating power from the measured total heating
current and an on-board electrical voltage of the motor vehicle; wherein
the heating power to be adjusted by the control device is readjusted
based on the momentary heating power and a set value.

7. The electrical heating device according to claim 6, wherein the device
for measuring the total heating current comprises a Hall sensor.

8. The electrical heating device according to claim 6, further comprising
a further non-volatile memory in which the on-board electrical voltage is
stored as a specified fixed value.

9. The electrical heating device according to claim 8, wherein the
further non-volatile memory is a programmable read only memory.

10. The electrical heating device according to claim 6, wherein the
on-board electrical voltage is transmitted as a message to the heating
device through a communication interface of the motor vehicle.

11. The electrical heating device according to claim 10, wherein the
communication interface is a vehicle bus.

12. The electrical heating device according to claim 6, wherein the
on-board electrical voltage is measured in the heating device.

13. The electrical heating device according to claim 6, further
comprising a comparator for determining a deviation of the momentary
heating power from the set value; and wherein the readjustment minimizes
the deviation of the momentary heating power from the set value.

14. The electrical heating device according to claim 1, wherein the
heating element is a PTC heating element.

15. A method of controlling an electrical heating device which comprises
an electrical heating stage with at least one heating element for heating
fluids in a motor vehicle, wherein the heating power is adjusted in fine
steps by modulating the current flowing through the electrical heating
stage; the method comprising activating the current through the
electrical heating stage for a specified time period within a specified
cycle frame, wherein the specified time period is a time period selected
from a plurality of time periods stored in a non-volatile memory; and in
the non-volatile memory, assigning a time period for the activation of
the electrical heating stage in each power stage of a plurality of
specified power stages.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electrical heating device for a
motor vehicle. The present invention particularly relates to an
electrical heating device which is especially suitable for a motor
vehicle the drive unit of which does not produce sufficient waste heat
for the heating nor the air conditioning of the vehicle passenger
compartment. This is the case for example with vehicles with an
electrical or hybrid drive.

[0003] 2. Description of the Related Art

[0004] An appropriate heating device must therefore be suitable for
providing both the interior of the motor vehicle with the required
thermal heat as well as making heat available for the running processes
in the individual system parts of the motor vehicle or at least providing
this demanded heat, such as for example for preheating the vehicle
rechargeable battery.

[0005] In the state of the art it is known that so-called resistance
heating elements or PTC (Positive Temperature Coefficient) heating
elements can be used for this purpose. They are self-regulating, because
they exhibit a higher resistance with increasing heating, thus allowing a
lower amount of current to flow for the same voltage. The self-regulating
properties of the PTC heating elements thus prevent overheating.

[0006] Accordingly PTC heating elements are often used in radiators which
are particularly used for heating the vehicle passenger compartment in
vehicles of this nature, the drive of which does not produce sufficient
process heat for the air conditioning or heating of the vehicle passenger
compartment. With hybrid vehicles a PTC heating device can also be used
as an auxiliary heater in the phases in which the internal combustion
engine is not running (for example at traffic lights or in a traffic
jam).

[0007] The air in the vehicle passenger compartment is heated with the aid
of the PTC resistance heating elements either directly (air heater) or
indirectly via a hot water circuit in which hot water flows through
radiators (hot water heating). In both cases a flowing fluid, i.e. a
liquid or gaseous medium, preferably water or air, is directly heated by
the heating elements.

[0008] An example of an electrical PTC heater with a plurality of heating
elements for a motor vehicle is known from DE 198 45 401 A1. The heating
power of one heating element can be continuously adjusted with a PWM
control whereas for all other heating elements it can only be switched
off or on completely in a binary manner.

[0009] In order to be able to optimally exploit power reserves in the
on-board supply system of a motor vehicle it is desirable to control an
electrical heating device so that the heating power is adapted as
accurately as possible to a specified power. This particularly applies to
vehicles with electrical propulsion in which the energy for the vehicle
drive and the electrical heating are supplied from the same source so
that a direct relationship exists between the operating range and the
available heating energy.

[0010] A linear power control for use at low on-board electrical voltages
(e.g. in the automotive low voltage range of approx. 12 volts or approx
24 volts) based on PWM (Pulse Width Modulation) functions such that the
electrical heating is controlled with a mark-space ratio (duty ratio)
proportional to the power demand. If for example 50% of the maximum
attainable power of a heating stage is to be reached, then the heating
stage is actuated with a duty ratio of 50%; for a 70% power demand this
is 70%.

[0011] The on-board electrical voltage in hybrid or electric vehicles may
be up to 500 volts and thus--from an automotive point of view--is in the
high voltage range. In the voltage range of a few hundred volts the
mark-space ratio is no longer proportional to the power. For example at
40% mark-space ratio 80% of the maximum power of a heating stage may
already be reached. Therefore the simple control described above cannot
be transferred without further ado to the automotive high voltage range.

SUMMARY OF THE INVENTION

[0012] The object of the present invention is to provide an electrical
heating device for heating fluids for a motor vehicle, in particular with
electrical propulsion, in which the heating power can be adjusted in fine
steps in a simple and robust manner to a specified power demand as well
as an appropriate adjustment method.

[0013] According to a first aspect of the present invention, an electrical
heating device for heating fluids for a motor vehicle, in particular with
electrical propulsion, is provided. The heating device comprises an
electrical heating stage with at least one heating element. Furthermore,
the heating device comprises a control device for adjusting a heating
power in fine steps by modulating the current flowing through the heating
stage. The heating device further comprises a non-volatile memory for
storing an assignment table, which assigns a time period for the
actuation of the electrical heating stage to each power stage in a
plurality of specified power stages. In order to adjust the heating power
of the electrical heating stage, the control device activates the current
through the electrical heating stage within a specified cycle frame for
the time period assigned to a power stage in the assignment table.

[0014] According to a second aspect of the present invention, a method of
controlling an electrical heating device is provided which comprises an
electrical heating stage with at least one heating elements for the
heating of fluids in a motor vehicle. The heating power is adjusted in
fine steps by modulating the current flowing through the heating stage.
The current through the electrical heating stage is in each case
activated for a specified time period within a specified cycle frame. The
specified time period is a time period that is selected from a plurality
of time periods stored in a non-volatile memory. In the non-volatile
memory, each power stage of a plurality of specified power stages is
assigned a time period for the activation of the electrical heating
stage.

[0015] The particular approach of the present invention is to equip a
heating device specially for the motor vehicle high voltage range with a
non-volatile memory for storing an assignment table. The assignment table
imparts a finely stepped assignment between an activation time within the
frame of a PWM and a heating power demand stage. With the assignment
table a non-linear power characteristic of a heating element can be
represented approximately by a piecewise linear curve. The more "base
points" are used, the more finely stepped is the heating power
adjustment.

[0016] Within the scope of the present invention, "finely stepped" is
taken to mean a step-by-step adjustment capability in a plurality of
steps, whereby the number of the steps is selected such that the power
differences in the first steps are small compared to the attainable total
power of the heating stage.

[0017] A control according to the present invention is particularly
suitable for heating elements with which the power produced increases
non-linearly with the mark-space ratio, as is the case with PTC heating
elements in the automotive high voltage range. In this case a simple
linear power control in which the relationship of the mark-space ratio
and power is identified by the value of a single proportionality factor
is not possible. According to a preferred embodiment an assignment table
is therefore used in which the relationship between the time periods and
the power values of the assigned power stages is non-linear. Hereby, the
non-linearity of the heating element is represented in step-by-step
linearised form.

[0018] In the assignment table each of a plurality of prescribed power
stages (nominal power rating) is assigned a corresponding time period for
the control of the heating element under a prescribed nominal on-board
electrical voltage. According to an example of a preferred embodiment the
total power of the first heating stage lies in the upper three-figure
watt range, e.g. 750 W. However, for example 1000 W or more is also
possible. In the example embodiment the number of the possible prescribed
power stages in this respect lies in the upper single-figure range, e.g.
7 or 8. According to an embodiment, in the assignment table the time
period of the activation within a fixed specified cycle frame is stored
directly as a time value, preferably in milliseconds (ms). In an
alternative embodiment the time period of the mark-space ratio is stated
as a percentage of the duration of the fixed cycle frame. The cycle frame
is a time duration (period) according to which the change of activated
and non-activated current (current switched on or off) is periodically
repeated.

[0019] According to a preferred embodiment the electrical heating device
furthermore comprises one or a plurality of further electrical heating
stages each with at least one heater element. With the further electrical
heating stages these are preferably so-called binary heating stages each
of which can only be switched between zero and a maximum power. The
heating power of the heating elements can be separately adjusted by the
control device via the current for the heating stages which flows in each
case through the heating elements. A control concept of this nature
facilitates a combined control with which binary heating stages are used
for the control of larger power stages. A smaller heating stage is
switched finely stepped (quasi-continuously) only for the fine
adjustment. In this way, in the high voltage range with the simple
control of the heating circuits (e.g. by a PWM signal) the normally
generated severe interference, e.g. due to EMC (electromagnetic
compatibility) emissions or wire-bound interference, is avoided.

[0020] Preferably, the non-volatile memory is a programmable read only
memory, preferably an EEPROM (Electrically Erasable Programmable Read
Only Memory).

[0021] In the high voltage range PTC resistances depend heavily on the
prevailing operating conditions, in particular the on-board electrical
voltage and the ambient temperature. It is therefore also desirable that
the power control of a PTC based device in the automotive high voltage
range includes a compensation of the non-linearity of the PTC
characteristic in view of the varying ambient temperatures and the
changing operating conditions.

[0022] Therefore the electrical heating device also preferably comprises a
device for measuring the total heating current flowing through the
heating device and a calculation device for calculating a momentary
heating power from the measured total heating current and an on-board
electrical voltage of the motor vehicle. In this embodiment the heating
power to be adjusted by the control device is readjusted based on the
momentary heating power and a set value. The fixed values for the
parameters of the heating power control stored in the assignment table
cannot by their nature take variations of the operating and ambient
conditions into account, but rather are based on previously defined
nominal conditions, in particular for the on-board electrical voltage,
ambient temperature and flow velocity. With the readjustment it is
possible to continuously fulfil a specified power demand as accurately as
possible even under varying operating and ambient conditions and with
heating elements with a non-linear characteristic.

[0023] Preferably, a Hall sensor is provided for the measurement of the
total heating current. This facilitates a simple, cost-effective and
robust current measurement. In comparison a current measurement in the
high voltage range in the motor vehicle using a shunt leads to high
interference so that no practicable measurement is possible. In the case
of a heating device for a motor vehicle with an on-board electrical
voltage in the automotive high voltage range of a few hundred volts the
Hall sensor is directly integrated into the control circuit in the low
voltage range. Thus, the current measurement value referred to the high
voltage range is immediately available for processing in the low voltage
range. Furthermore, a prescribed isolation between the control circuit
with the low voltage and the load circuit in the high voltage range is
maintained.

[0024] According to a preferred embodiment the heating device has a
further non-volatile memory in which the on-board electrical voltage is
stored as a prescribed fixed value. Also preferably, the non-volatile
memory is a programmable read only memory, preferably an EEPROM. In the
EEPROM the on-board electrical voltage is saved in the software or
firmware. The non-volatile memory can furthermore be preferably
integrated into a non-volatile memory in which the assignment table is
stored. However, it is also possible to provide a non-volatile memory
separately for the assignment table and the on-board electrical voltage.

[0025] According to an alternative preferred embodiment the on-board
electrical voltage is communicated via a communication interface of the
motor vehicle as a message to the heating device. The communication
interface is preferably a vehicle bus (e.g. a CAN (Controller Area
Network) bus or LIN (Local Interconnect Network) bus).

[0026] According to a further alternative preferred embodiment the
on-board electrical voltage is directly measured in the heating device.
This preferably occurs on the circuit board, that is on the high voltage
side. The measurement can take place permanently or at predetermined time
intervals.

[0027] According to a preferred embodiment the heating device furthermore
comprises a comparator for the determination of a deviation of the
momentary heating power from the set value. The readjustment occurs on
this basis such that the deviation of the momentary heating power from
the set value is minimised.

[0028] Preferably switchover of the further heating stages by the control
device can be used for adaptation of the power consumption to the set
value.

[0029] Preferably, the on-board electrical voltage is in the automotive
high voltage range, in particular in the range from 200 V to 500 V. For
example, for vehicles with electrical propulsion on-board electrical
voltages of about 300 V to 400 V, for example 350 V, are usual.

[0030] According to a preferred embodiment the heating elements are PTC
(Positive Temperature Coefficient) heating elements.

[0031] Furthermore, the readjustment is implemented according to a
preferred embodiment with the aid of a closed-loop control device which
comprises a microcontroller. According to the preferred embodiment the
closed-loop control is realised in the microcontroller on the low voltage
side.

[0032] Further advantageous embodiments of the present invention are the
subject matter of dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is described in the following based on the
accompanying figures in which:

[0034]FIG. 1 shows an example illustration of an air heater for the
automotive high voltage range with integrated electronic components;

[0035]FIG. 2 illustrates a schematic construction of a circuit board with
mounted electronic control means and a power switch for a high voltage
air heater with integrated electronic components;

[0036]FIG. 3 shows the schematic basic construction of an electrical
heating device according to an embodiment of the present invention;

[0037]FIG. 4 shows further details of the construction of an electrical
heating device according to an embodiment of the invention;

[0038]FIG. 5 illustrates an example of an assignment table for the
control of the first heating stage according to an embodiment of the
present invention; and

[0040] The present invention relates to an adjustable electrical
motor-vehicle heater, which can preferably be formed as an air or hot
water heater.

[0041]FIG. 1 shows the outer construction of an example of a heating
device 100 according to the present invention. As an example, FIG. 1
shows an air heater for the automotive high voltage range with integrated
electronic components. The individual heating elements are built into the
housing frame shown on the right side of the drawing. The integrated
electronic control means is located in the terminal box located on the
left.

[0042] Details of the outer construction of the electronic components are
illustrated in FIG. 2. FIG. 2 shows a modular construction of the
electronic means in sandwich form in which the various modules are
interconnected via a circuit board 210. In particular this refers to the
electronic control means 220 and the power switch 230. The electronic
control means 220 comprises components for open-loop and closed-loop
control according to the present invention. In particular the power
switches 230, as constituent parts of the control device according to the
invention, are used for the direct adjustment of the heating power by
switching a controlled current on and off through the heating elements of
a heating stage, the heating elements being respectively assigned to the
power switches. Further details of the construction of the electronic
means according to an exemplary embodiment are explained in conjunction
with FIG. 4.

[0043]FIG. 3 shows an example of a schematic construction of a heating
device according to the present invention. In the illustrated example the
heating device comprises four heating stages 1 to 4. The four heating
stages comprise a first heating stage 330 and (in the illustrated example
three) further heating stages 335. According to the invention the first
heating stage 330 can be controlled stepwise (quasi-continuously) in
small steps. The other heating stages 335 are binary heating stages, the
power of which can be switched between zero and a maximum value. A group
of power switches 320 provides direct control of the heating stages. The
power switches are each assigned to one of the heating stages. For the
control of the power switches the electronic control means 310 is
employed which according to a preferred embodiment is implemented as a
microcontroller.

[0044] Here, a first adjustment of the heating power can occur according
to a power demand assuming nominal conditions for the operating and
ambient parameters. Examples of the manufacturer's set nominal conditions
are, for example, an on-board electrical voltage of 350 V and the
assumption of an air temperature of 0° C. with an air heater.
Furthermore, the nominal conditions also include a specified flow
velocity (for example an air flow rate of 300 kg/h or 10 l/min for a
liquid medium). The control parameters required for fulfilling a
specified power demand under nominal conditions are laid down by the
manufacturer. This can take place, for example, in the form of firmware
or software in an EEPROM.

[0045] For the adaptation to the operating conditions and changed ambient
conditions the power (nominal value) preset in the first step is adapted
to the accurate power demand by readjustment. For this purpose a
closed-loop control device is integrated into the electronic control
means 310, with the aid of which a closed-loop control circuit for the
readjustment of the heating power set by the control device is realised.
Alternatively, within the scope of the present invention it is also
possible to provide the closed-loop control device in separate hardware.
For the readjustment the closed-loop control device requires the value of
the on-board electrical voltage 350, the specified set value 370 for the
power to be consumed by the heating device and the measured value of the
total heating current 360. The total heating current includes the value
of the current averaged over a cycle frame or a plurality of cycle frames
for a heating stage controlled by means of the modulation of the current
(e.g. PWM). The averaging can take place by means of software in a
microcontroller.

[0046] The on-board electrical voltage 350 can here be made available in
different ways.

[0047] According to a preferred embodiment the on-board electrical voltage
can be stored as a fixed value, for example in an EEPROM. In this respect
a preliminarily preset nominal value for the on-board electrical voltage
is used. An embodiment of this nature can be realised particularly
cost-effectively. However, it has the disadvantage that the momentary
actual value of the heating power cannot be exactly determined, because
deviations of the on-board electrical voltage from the nominal value are
not taken into account in operation.

[0048] Alternatively, the on-board electrical voltage 350 in the vehicle
on the heating device circuit board can be directly measured. Thus the
disadvantage of the embodiment mentioned above is eliminated, because
with each change of the on-board electrical voltage in operation the
present value can be provided very quickly. A disadvantage of this
embodiment is however the higher costs arising due to the specially
provided voltage measurement device on the heater.

[0049] A further alternative is possible with the provision as a message
from the motor vehicle on-board network via a vehicle bus. The on-board
electrical voltage 350 is continuously acquired in the vehicle and made
available via the on-board supply system. This embodiment represents in
this respect a compromise as it is more economical than the direct
measurement, but takes the changes into account more slowly. With this
embodiment an updated value of the on-board electrical voltage 350 is
available only every 200 to 300 ms.

[0050] The closed-loop control device 310 receives the heating power
demands 370, for example, from the vehicle on-board network via the
vehicle bus (for example LIN or CAN data bus). They can for example be
automatically defined such that existing power reserves of the on-board
supply system are exploited as completely as possible. They can also be
specified by the driver via the air conditioning operating panel.

[0051] Alternatively, it is also possible to specify a desired temperature
instead of the power demands 370. This may be, for example, a temperature
at a certain part of the vehicle, such as an interior compartment
temperature or a temperature of the flowing medium. The temperature
demand 220 is converted by the control electronic means 220 into a power
demand 370.

[0052] With the aid of the on-board electrical voltage 350 and the total
heating current 360 the consumed power (actual value) is first
determined. For this purpose the measured current 360, where necessary
suitably averaged over time, for example over one or a plurality of cycle
frames, is multiplied with the on-board electrical voltage. The actual
value of the total heating power is given according to the equation

P=U×I,

according to which the electrical power P consumed by a component (here:
the total of the heating stages of the heating device 100) is equal to
the product of the voltage U applied to the component and the total
current I flowing through the component. The actual value of the
momentary total power of the heating device 100 determined in this way is
then compared to the specified power demand (set value) by a comparator
implemented in the closed-loop control device. Based on this the control
device is initiated to correct the power consumption by an appropriate
adaptation of the heating power setting. In a preferred embodiment the
new heating power (nominal value) to be set corresponds to the previously
set nominal value reduced or increased by the set value deviation. The
correction takes place first of all via the setting of the
quasi-continuous first heating stage 330. Depending on the demand the
switching of the further binary heating stages 335 on and off can
furthermore be included in the correction adaptation of the heating
power.

[0053] In this way the prescribed nominal value of the heating power is
continuously adapted for readjustment in the closed-loop control circuit.
By means of this explained concept the heater always accepts a
readjustment of the power in the direction of the set value. Through
appropriately defined and temporally variable power requirements the
readjustment can furthermore also be used to always exploit the maximum
power reserves available in the vehicle.

[0054] A detailed illustration of the main elements of a controllable
heating device according to the invention is shown in FIG. 4. According
to the embodiment illustrated in FIG. 4 the heating device comprises a
load circuit with a supply voltage in the automotive high voltage range
420 and a control circuit with an operating voltage in the low voltage
range 430. Both ranges must be electrically well isolated from one
another (basic isolation). Here, the high voltage and low voltage ranges
on the PCB (Printed Circuit Board) 440 are in particular isolated from
one another. A current measurement (measurement of the total current
flowing through the heating device) is in this case, in a particularly
simple manner and without affecting the electrical isolation, carried out
by electromagnetic means with the aid of a Hall sensor 400 (indirect
current measurement).

[0055] The microcontroller 310 processes the measurements as well as the
fixed values specified in the system, such as the on-board electrical
voltage or the assignment table for the quasi-continuous power control of
the first heating stage by means of PWM. The EEPROM 410 is exemplarily
illustrated as a memory device for the system parameters of this nature.
In the present embodiment the group of control elements 320 for each of
the heating stages 330, 335 (here represented in each case by a PTC
heating element) comprises separately controllable power switches,
preferably realised as IGBT (Insulated Gate Bipolar Transistor) power
switches. The IGBT power switches operating in the high voltage range are
controlled by IGBT drivers which in turn receive their control signals
from the microcontroller 310 on the low voltage side. Preferably the
switch group 320 with all IGBT drivers and IGBT switching transistors is
accommodated in a common housing.

[0056] A detailed description of an exemplary open-loop and closed-loop
control concept according to the present invention follows. A special
exemplary embodiment is explained for the power control of a heating
stage controllable in small steps (quasi-continuous) with reference made
to the assignment table 500 illustrated in FIG. 5.

[0057] The control occurs using a method which is principally based on PWM
(Pulse Width Modulation), but has been modified particularly to
facilitate a use of heating elements with a non-linear power
characteristic, such as for example PTC elements. The maximum power in
the example in FIG. 5, 750 W, is here achieved through permanently
switching in the first heating stage (refer to Stage 1 in FIG. 6, max.
750 W). This means that the time period of the control is equal to the
length of the cycle frame or expressed differently, a mark-space ratio
(duty ratio) of 100%. It can also be alternatively achieved through
permanently switching in the second, binary heating stage with 750 W of
power with the first heating stage switched off. The control concept is
further explained with reference to FIG. 6. In the EEPROM a discrete map
is stored with--in the above example of FIG. 5 (for Stage 1 in FIG.
6)--eight power stages.

[0058] With a conventional PWM a mark-space ratio proportional to the
demanded power is used. If, for example, the power demand is 50% of the
maximum power consumed by the heating stage, then a control with a
mark-space ratio of 50% is carried out within a fixed cycle frame. A
control of this nature (mark-space ratio proportional to the power
demand) corresponds to a linear dependence of the power on the mark-space
ratio. However this is not present in the automotive high voltage range.
In a typical example of PTC heating elements used at approx. 350 V 80% of
the nominal power is already achieved under nominal conditions with a
mark-space ratio of 40%. The relationship between the mark-space ratio
and nominal power can however have a completely different non-linear
progression, as illustrated for example in FIG. 5.

[0059] In contrast to the conventional PWM, with the special control
concept portrayed here individual power stages and corresponding
activation times within a cycle frame are stored as fixed values in the
electronic control means of the heating device. This occurs in the form
of a table (assignment table) with a number of pairs of values which on
one side specify the power to be set and on the other side the activation
duration required for this.

[0060] A simple example of an assignment table 500 of this nature is shown
in FIG. 5. In the left column 510 the individual controllable power
stages (nominal powers corresponding to nominal conditions) are stored as
fixed values. As can be taken from the listed exemplary table 500, in
this example the maximum power consumption of the heating stage (with
permanent actuation) is 750 W. The range from 0 to 750 W is divided into
eight stages so that a finely stepped (quasi-continuous) adjustment of
the heating power is possible with steps below 100 watts.

[0061] In the right column 520 of table 500 the control times assigned to
the respective nominal power stages are stored in milliseconds. The
control of the heating stages occurs such that depending on the power
demanded the heating stage is activated for the assigned time period by
switching on the flow of current at the prevailing on-board electrical
voltage. As with conventional PWM, the activation is repeated with a new
cycle frame. The length of the specified fixed cycle frame is 170 ms in
the present example. The length of the cycle frame is however not
important for the invention. Also, completely different cycle frame
lengths of, for example, 150 ms or 200 ms or even cycle frames with a
completely different order of magnitude are possible.

[0062] In this way the relationship between the heating power demand and
the stored activation duration per cycle frame in the assignment table
can be arranged as required. Thus, the non-linearity of a PTC heating
element in the high voltage range can in particular be compensated. For
this purpose the corresponding activation times are determined
empirically beforehand and stored in the EEPROM 410 by the manufacturer.
The nominal powers and the associated empirically determined activation
times correspond to defined nominal conditions, i.e. in particular a
specified on-board electrical voltage (e.g. 350 V) and a fixed ambient
temperature around the heating element (e.g. 0° C.). Due to the
previously defined table of values, within the scope of this control no
adaptation occurs to currently changing operating parameters and in
particular no temperature compensation, which in practice leads to
tolerances in the range of about 30% maximum. This disadvantage with the
above described simple and robust control of the power stages of a
quasi-continuous heating stage is compensated in the scope of the present
embodiment with good approximation due to the continuous readjustment
based on a comparison of set and actual values, as described above. Here
it is particularly considered that also the deviation of the real ambient
conditions as well as other operating parameters such as the on-board
electrical voltage and the flow velocity may continuously change from the
nominal conditions in real operation.

[0063] Normal voltage variations in on-board supply systems in the
automotive high voltage range lie in an order of magnitude of 100 V.
Electric vehicles have for example a nominal voltage of 350 V. After
charging the battery the on-board electrical voltage may rise to approx.
380 V and on discharging drop to approx. 280 V. Electric vehicles with a
different nominal voltage on the on-board supply system, for example 400
V also have a corresponding variation. For hybrid vehicles the nominal
voltage is approx. 288 V, the maximum on-board electrical voltage is
approx. 350 V and the minimum voltage approx. 200 V.

[0064] Due to monitoring of the actual heating power applied, the
closed-loop control according to the invention can principally also be
used in 12 V on-board supply systems. However a voltage variation with 12
V on-board supply systems (for example up to 12.5 V) only plays a minor
role for the heating power. Essentially, the current level is decisive
(substantially higher than in the automotive high voltage range). In
addition, with the materials used for PTC heating elements (for example
similar to ceramics based on barium titanate) in the automotive high
voltage range there is a semiconductor effect, according to which the
resistance is not just temperature-dependent, but also voltage-dependent.

[0065] The adjustment of the power stages by the control device therefore
occurs on the basis of nominal powers corresponding to nominal
conditions. The approximation of the real heating power to the power set
value occurs through the readjustment in the closed-loop control circuit.
Here, to minimise the difference between the actual and set powers
determined by the comparator a nominal power is switched on and off
according to the difference.

[0066] Within the scope of the control concept explained above it is
furthermore also possible to control higher total heating powers in fine
steps. For this purpose a combination of a finely stepped controllable
first heating stage with further binary heating stages is used as
mentioned above in connection with FIGS. 3 and 4.

[0067] As an example, the control of power values between 0 and 6000 watts
with the aid of such a combination is illustrated in FIG. 6. A total of
four heating stages are provided. The first (quasi-continuous) heating
stage has in the present example a maximum power consumption of 750
watts. The power consumptions of the binary heating stages are as
follows: second heating stage: 750 watts, third heating stage: 1500 watts
and the fourth heating stage: 3000 watts.

[0068] In the range from 0 to 750 watts a finely stepped control, as
described above, is only possible by using the first heating stage. In
the following range between 750 watts and 1500 watts (i.e. again a range
of 750 watts) the second heating stage is switched on in a binary manner,
whereas the first heating stage supplies the fine control within this
range according to the above concept. In the following range comprising
750 watts (from 1500 watts to 2250 watts) this occurs analogously with
the switching on of the third heating stage, whereby the second heating
stage is switched off again. The second and third binary heating stages
are switched on simultaneously in the following range between 2250 watts
and 3000 watts. From 3000 watts the fourth heating stage is switch on
permanently so that analogously, as described above for the range below
3000 watts, the heating power in the whole range up to 6000 watts can be
controlled in fine steps over a total of 64 steps (corresponding to the
"points" on a step-by-step linear representation). The number of steps
(here: 8 for a single heating stage up to 750 W and 8×8=64 in the
total range covering 8×750 W=6000 W) is however only used as an
explanatory example. Preferably more than 50 steps, for example between
50 and 100 steps, are used. However, more than 100 steps and also a
substantially greater number of steps is possible, for example
approximately 200 steps. The more partial steps are used, the finer is
the resolution for the adjustable heating power.

[0069] A control concept of this nature means that the PWM cycling is only
required in a first heating stage which comprises the smallest power
range, whereas in the higher power range a simple binary control occurs.
The use of the PWM only occurs for the fine-setting closed-loop control.
In this way interference in the high voltage range through EMC emission
is largely avoided. The cycling frequencies of the quasi-continuous
heating stage are furthermore optimised with regard to the EMC/ripple
current. Generally, a finer resolution of the partial steps also causes
less interference in the high voltage on-board supply system.

[0070] Summarising, the present invention relates to an electrical heating
device for motor vehicles, in particular with electrical propulsion. The
heating device according to the invention uses a PWM based control
concept which can be used for heating elements with any non-linear
characteristics. In this respect activation times in a cycle frame are
assigned to power stages to be controlled and are stored in a table in a
non-volatile memory.

Patent applications by Dieter Emanuel, Annweiler DE

Patent applications by Holger Reiss, Rheinzabern DE

Patent applications by Eberspacher catem GmbH & Co. KG

Patent applications in class Comprising timing or cycling means

Patent applications in all subclasses Comprising timing or cycling means